Radiation-induced changes in the density and viscosity of 30% TBP-n-dodecane-HNO3 mixtures were examined. The increase in the density becomes significant with increasing nitric acid content of the solvent, [HNO3](TBP), and absorbed radiation dose, which concomitantly leads to a much sharper increase in the viscosity of the solvent. The extent of increase in the viscosity is significantly enhanced by gamma radiolysis and is a function of absorbed dose. These changes are attributed to radiation-induced polymerization and nitration of the hydrocarbon diluent as revealed by gas-liquid chromatography (GLC) and infrared (IR) assay of the solvent. Various possible modes of hydrogen bonding seem to play a major role in enhancing the viscosity of the system. Efficacy of solvent purification by alkaline scrub followed by alumina treatment is described in terms of the amount of degradation species retained in the treated solvent. Interestingly, the small amount of radiolytic species remaining in the solvent due to incomplete solvent purification causes a considerable increase in the viscosity of the solvent.